Fix below warning when CONFIG_OF=n:

drivers/regulator/pwm-regulator.c:393:34: warning: ‘pwm_of_match’ defined but not used [-Wunused-const-variable=]
  393 | static const struct of_device_id pwm_of_match[] = {
      |                                  ^~~~~~~~~~~~
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Link: https://lore.kernel.org/r/20200821111658.59a7218b@xhacker.debianSigned-off-by: Mark Brown <broonie@kernel.org>